Digital Color Management: Encoding Solutions, 2nd Edition

10

Densitometric Color Encoding

Densitometric color encoding is based on input-image color measurements made according to defined sets of spectral responsivities that are not equivalent to a set of visual color-matching functions. The responsivities can be those of a particular type of densitometric instrument, such as an ISO Status A or Status M densitometer (Figure 10.1). The responsivities also can be those of an actual scanner or of some hypothetical reference scanner. Encoded colors can be expressed in terms of red, green, and blue densities, transmittances, reflectances, CMY or CMYK colorant amounts, or other values associated with the densitometric measurements.

The principal advantage of this type of encoding is that, because it corresponds quite directly to physical measurements of input images, it often simplifies color signal processing. Consider, for example, the system shown in Figure 10.2. Let us assume that the objective of the system is to produce output images that visually match scanned input images, and also that the output thermal print medium has CMY image-forming dyes that are identical to those of the input medium.

The responsivities of the system's densitometric scanner can be designed such that each R, G, or B channel primarily “sees” just one image-forming dye of the input medium (Figure 10.3). Each scanner color signal therefore will represent the amount of the corresponding C, M, or Y dye for each pixel in the scanned image. If the output is also designed ...